CNT has been the research focus over a decade due to its unusual properties, which are valuable for nanotechnology, electronics, optics and other fields of materials science and technology. In particular, owing to their extraordinary thermal conductivity and mechanical and electrical properties, CNT finds applications as additives to various structural materials.
Presently, CNT can be produced in large quantities by these following dominant techniques: chemical vapor deposition, high-pressure carbon monoxide process, arc discharge, and laser ablation. Hydrocarbons decomposition over Ni, Fe, or Co catalysts has been recently investigated by some researchers to produce CNT. It has been reported that multiwalled CNT with inner diameters 5 nm to 10 nm can be formed during ethylene decomposition at 700° C., atmospheres pressure over Co and Fe catalysts. In addition, multi-walled carbon nanotubes have been produced that have 5 to 20 nm inner diameter and 60 to 413 nm in length, which were synthesized over nickel supported on a zeolite by the decomposition of methane in the relatively low temperature range 400-550° C. Nevertheless, almost all produced CNTs have an inner diameter from 5-20 nm.